Urea-aldehyde resin adhesives and process

ABSTRACT

This invention relates to the method of bonding water-penetrable cellulosic substrates with urea-aldehyde resin adhesives as illustrated by bonding of wood flakes into particle boards, and in particular to a method of improving the efficiency of said adhesives, which comprises replacing from about 1 up to about 35% by weight of the resin solids by a salt selected from the group consisting of alkali and alkaline earth halides and mixtures thereof; and to the resultant products.

United States Patent 1191 Black [4 1 Sept. 16, 1975 UREA-ALDEHYDE RESIN ADHESIVES AND PROCESS [75] Inventor: William Raymond Black,

Springfield, Oreg. [73] Assignee: Borden, Inc., Columbus, Ohio [22] Filed: Apr. 23, 1971 [21] Appl. No.: 137,036

Related U.S. Application Data [62] Division of Ser. No. 797,253, Feb. 6, 1969, Pat. No.

52 U.S. c1. 156/622; 156/242; 156/331; 428/326; 428/407; 264/109 51 1m.c1. ..B29J 5/00 [58] Field of Search 156/622, 242, 331; 264/109, 128; 260/294 R; 161/68 [56] References Cited UNITED STATES PATENTS 2,175,475 10/1939 Ludwig 260/294 R 2,772,197 11/1956 Kozdemba 156/331 Ryan et a1 156/331 Goldstein et a1 156/319 3,391,233 7/1968 Polovtseff 156/622 3,428,505 2/1969 Siempelkamp. 156/622 3,442,999 5/1969 Konig et a1. 264/109 3,450,659 6/1969 Bondi et a1... 260/294 R 3,490,969 1/1970 Schiff 156/622 3,554,856 1/1971 Opferkuch et a1. 156/622 3,563,844 2/1971 Brown 156/622 Primary Examiner-George F. Lesmes Assistant Examiner-Paul .1. Thibodeau Attorney, Agent, or Firm-George P. Maskas; George A. Kap

[5 7] ABSTRACT 6 Claims, N0 Drawings- BACKGROUND OF THE INVENTION In bonding water-penetrable cellulosic particles such as was d chips with adhesives comprising urea-aldehyde resins, there is an urgent need for improving adhesive efficiency. The industrial success of particle board manufacture, for example, depends largely on achieving high levels of bond strength at relatively low cost. Toward this end, it is therefore desirable to exploit the availability of cheaper wood-waste material such as plywood trim. But the inclusion of waste materialin the wood 'furnish often tends to impair the uniformity of bond strength and to lower flie average strength when conventional amounts of urea-aldehyde adhesive are used. While strength may be improved by increasing the amount of resin applied, this defeats the purpose of economy.

Even as regards the higher grades of particle board manufactured from specially selected wood furnish carefully engineered as to particle size and shape of wood chips or flakes, there is a growing demand for products with still further increased strength to meet new use requirements. When these-requirements are met by using increased amounts of resin adhesive, th costs again tend to become prohibitive.

Bond strength may be increased somewhat by bonding at higher temperature and pressure but the resultant improvement is not sufficient to permit including plywood trim or high levels of many other waste materials in the furnish.

SUMMARY OF'THE INVENTION A process has now been found whereby ureaaldehyde resin adhesives are capable of bonding waterpenetrable cellulosic substrates with lower amounts of resin solids into products, such as particle board, without impairment of strength. a,

In brief, the present invention comrises replacing from about 1 up to about 35% by weight of the resin solids normally applied in bonding water-penetrable cellulosic substrates by a salt selected from the group consisting of alkali and alkaline earth halides and mixtures thereof. The invention also includes ureaaldehyde adhesives comprising the replacing salts, and also includes the resultant products. l I

In addition to the advantage that suitablechoice of the replacing salt may effect substantial savings in ma terial costs without loss of adhesive strength, it has been surprisingly found that tensile strength in many cases is substantially increased at the same level of total solids add-on and without changing the temperature and pressure of curing. It has furthermore been found that high and uniform strength may be obtained even when the wood furnish comprises upto 50% by weight of waste material such as plywood trim.

DETAILED DESCRIPTION The substrate material" to be bonded in carrying out I 2 losic, a term intended to include lignocellulosic. While the advantages of the instant invention are illustrated ,herein with particular respect to the manufacture of particle board, the modified adhesives of the invention may also be used to advantage in the gluing of wood in laminar form, such as in laminating wood ply to particle board or to other wood ply V Substrate material may thus be derived from pine, fir, hemlock, spruce, beech, lime, poplar, ash, chestnut, kimba, gaboon, or other tres. When these are used in the manufacture of particle board they are comminuted into the form of particles such as chips or flakes.

Thestarting material for such comminution may be whole wood or may include peeler cores, veneer residues, plywood trim, slats, edgings and the like and'may also include minor amounts of non-woody cellulosic materials, such as bagasse, flax shives, bamboo or straw. In addition to the cellulosic particles there may also be included a minor proportion of porous plastics of compression-resistant properties such as small beads comprisingan expandable or expanded styrene copolymer. I T he urea-aldehyde resin for use in the bonding may for example be any acid-curable condensation product of formaldehyde with urea in mole ratio corresponding to1-2 moles formaldehyde to 1 mole urea. All or part of the formaldehyde maybe. replaced by other aldehydes such as acetaldehyde, propionaldehyde or furfural. Abo ut 550% by weight of the urea may be replaced by melamine. l

A typical resin adhesive according to the instant invention is made by charging 53 parts of 50% aqueous formaldehyde solution and2 3 parts of urea to a reaction kettle. The solution is first neutralized to a pH of 7.0-8.0 then heated to reflux temperature and refluxed for 20-60 minutes. After acidification to pH 5.0-6.5, condensation is continued until a Gardner bubble tube reads between A and C At this point pH is brought to 7.0 then 12 parts of urea are charged and the clear solution cooled to 20 s0c.

In adjusting pH during the manufacture of theresin adhesive, any appropriate acid or base may be used, as

for example formic acid and sodium hydroxide respectively. I Q

To convert the urea-formaldehyde resin thus ob tained to, a modified adhesive according to this invention, there is then charged to the kettle a halide salt in solid, solution or slurry form, as for example a solution of 8 parts of lithium chloride in 4 parts water. Agitation is continued until a clear solution is obtained which is then cooled for storage. Typical batches of material made. in this way have viscosity between 200-400 cps., pH between 6.8-7.5 and solids between 66-68% by weight. w v

The halide salt of this invention may be any soluble halide of an alkali or alkaline earth metal. Because of their present relative cheapness sodium chloride and magnesium chloride are currently preferred, but salts which function according to this invention include, for

example, potassium chloride, lithium chloride, sodium bromide, potassium iodide, magnesium bromide, calcium chloride, strontium chloride and barium chloride.

The salt of this invention may be first mixed with the urea-aldehyde resin, as above illustrated, and applied simultaneously with the resin to the material to be bonded. Alternatively, an aqueous solution of the salt may be separately applied to the substrate either before or after the resin; Thus for example, the salt may be incorporated in a wax dispersion applied to impart water resistance.

In addition to the urea-aldehyde resin and the salt of this invention, the usual substances may be added to the adhesive in the requisite minor quantities for the purpose of accelerating cure of the resin or for the purpose of imparting certain properties on the finished product such as water resistance, fire retardance, or resistance to mold and fungi. As to accelerators for the curing of the resin, these could be any suitable acid or acid donor such as are commonly used with ureaaldehyde resins,'and include formic acid, ammonium chloride, ammonium sulfate and zinc chloride. Western soft woods commonly contain a sufficient level of acidic material in nature to make the addition of such accelerators unnecessary in their case.

The simultaneous or stepwise application of the various aforementioned additives, including the resin and the halide salt of this invention, may be carried out in either batch-wise or continuous manner using machinery well established in the relevant manufacturing arts, special care being taken to effect homogeneous distribution of all said additives.

, As to amounts, the total of additive solids including urea-aldehyde resin and halide salt is usually in the range of from 3-15 parts per 100 substrate material. The preferred amount is to be determined by the necessity for balancing cost against specific efficiency and is usually in the range of about 5-7 parts per 100 of sub strate material. Some of the advantages of using the salt of this invention,'particularly from the standpoint of savings in cost, may be obtained when as little as 1% by weight of the resin solids is replaced by halide salt. The minimum amount required to obtain substantial increase in bond strength is dependent on the nature of the substrate material and may be approximately about 2-3%. As the proportion of halide salt is increased incrementally above this threshold, bond strength is correspondingly increased over a range that is specific to the particular substrate, eventually reaching a maxi mum level of bond strength. While further increases in proportion of halide salt do not further enhance the strength, up to about 35% replacement of resin solids bysalt may often be used satisfactorily without adversely affectingthe properties of the bonded product.

After the modified adhesive and any other additives as aforementioned have been distributed between the juxtaposed surfaces to be bonded, the bonding is effected by curing of the resin at elevated temperature and pressure, these conditions being kept sufficiently mild to avoid degradation of the particular substrate materialfln the case of particle board the substrate particles are first consolidated by pressing into desired shape. The conditions chosen for curing of the resin will depend on parameters familiar to those skilled in the art, including the nature of heat exchange which among other factors depends on the density and thickness of the assembly to be bonded. Commonly used conditions fall within the ranges 280425F. (platen temperatures), 50-800 psi. and 220 minutes curing time, but the advantages of the instant invention could conceivably be attained under conditions other than these. v v

The mechanism throughwhich this invention is operative is not completely understood. It appears not to be connected with any'catalysis of curing inasmuch as the augmented strength is obtainable with inert salts such 4 as sodium chloride, potassium bromide and lithium chloride which are known to be without catalytic effect on the curing of urea-aldehyde resins.

In the examples that follow and elsewhere herein, proportions are expressed as parts by weight unless specifically stated to the contrary.

It is well-known to those skilled in the art that moisture contained in the wood has a vital role in bonding of wood by urea-aldehyde resins and the level of water content should be closely controlled. While amounts of add-on are given in the following examples on the basis of oven-dried wood, the substrate chips which were treated as described in the examples below contained between 3 and 6% moisture. in comparison tests, aliquots of substrate were used having the same water content. To obtain optimum performance with any particular blend of wood furnish, it is common practice to study the effect of water content on adhesive efficiency over a range of moisture levels to determine the preferred level. V

EXAMPLE 1 A furnish of Ponderosa pine and 25% Douglas fir was reduced to particles in a Bauer attrition mill. A furnish of white fir was reduced to chips in a Pallmann pulverizer. A 50-50 blend of these two furnishes was used in the experiments of Examples 1, 2, 3 and 4. An aliquot of these flakes was treated with a catalyzed ureaformaldehyde resin, (Casco Resin WS-1l4-79) in amount corresponding to 6 parts by weight resin solids per 100 parts oven-dry wood, using a horizontal rotating drum-type blender with internally mounted spray system. There was then likewise added 0.5 parts of a paraffin wax emulsion, care being taken to attain maximum homogeneity. Square samples of board of dimension 14.5 X 14.5 inches and 0.838 inches in thickness were preformed by mat consolidation at a pressure of 250 psi. prior to the final pressing and curing at 310F. for 5 minutes. During this pressing cycle the pressure varied from about 650 psi. down to about 50 psi. This example illustrates a treatment not including the halide of this invention and tests on the product thereof are included for comparison in Table I together with corresponding data on the products of the following examples 2, 3 and 4.

. EXAMPLE 2 EXAMPLE 3 The procedure of Example 1 was followed except that 6 parts by weight sodium chloride were added to 100 parts of liquid Casco Resin WS-l1479 and this mixture was used to treat the wood flakes in amount corresponding to 6 parts by weight total solids per 100 1 parts of oven-dry wood. This treatment differed from Example 1 in that 9% of the resin solids were replaced by sodium chloride.

EXAMPLE 4 The procedure of Example 1 was followed except that 3 parts by weight magnesium chloride (MgCl were added to 100 parts of liquid Casco Resin WS-l 1- Table II Effect on Adhesive Efficiency of UF Resin When 6% Sodium Chloride (based on liquid resin) is used Instead of Catalyst in Amount of Ammonium Sulfate.

EXPERIMENT A B C 4-79 and this mixture was used to treat the wood flakes in amount corresponding to 6 parts by weight total L)? S s d n ad. solids per 100 parts of oven-dry wood. Since the solids f we'ght i None I NaCI based on liquid resin none none 6% content of Casco Resin WS-1l479 was 60%, this Board thickness, inches .814 .808 .814 treatment differed from Example 1 in that 4.8% of the Density lbs/cu'fi- Internal bond strength, psi. 92 I22 I 16 resin solids were replaced by magnesium chloride. Modulus f rapture 2260 2346 2466 Test results on the particle board products of Examples 1 through 4am summarized in Table I. These re- EXAMPLES 6 7 and 8 sults show significant improvement in the internalbond strength achieved by the incorporation of the respec- A fumlsh Composed f y of Ponderosa Pme was tive alkali halides in place of part of the resin. solids. reducad to flakes and ahquots were treated p tively as indicated in Table Ill. The procedure was essentially that of Example 1, excepting that the UF resin Table I used was Casco Resin WSl38-44 containing 65% solids and the combined resin and halide solids applied Effect of alkali halides on UF Resin Efficiency using n n oven-dry basis Was 5.5%. A paraffin wax emul- Casco Resin WS-1l4-79 (60% solids) and wood chip sion was applied at 0.5% level on oven-dry basis. Treatblend containing 37.5% Ponderosa Pine, 12.5% Dougment as carried out in rotating drum blender las Fir and 50% White Fir. All treatments at 6% total q pp with Internal p y Particle board Samples lid n b i of oven-dried wood weight. were pressed for 4.5 minutes at 325F. and under 50650 psi. Example 6 was a control sample prepared without any alkali halide. Examples 7 and 8 illustrate 2 3 4 the instant invention and differed from each other in EXAMPLE I t Alkali halide None MO MCI Mgclg that the sodium chloride in Example 7 was first mixed with the resin before spraying, whereas in Example 8 an Parts y w ight f r 0 v aqueous solution of sodium chloride was first sprayed 8 3 2 on the furnish, the furnish was then redried to the initial Density (lbs/Cult.) 41.5 42.2 42.4 42.3 mixture content and the resin was then applied. lnlemfl' (Psi-l 95 The results of corresponding tests, as summarized in Table III show that internal bond strength was substantially increased by the replacement of 8.25% of resin X PLE 5 solids by sodium chloride both when the sodium chloride was a lied simultaneous] with the resin and also A furnish of 100% White Fir was reduced to chips in y a when the resin and sodium chloride were applied sepaa Pallmann pulverizer. Using the blender and spray 4O rately Table II] Effect of mode of addition of Sodium Chloride on Adhesive Efficiency of 21 UP Resin EXAMPLE 6 7 8 No NaCl NaCl Added NaCl Added Procedure With Resin Separately Board Thickness, Inches .825 .814 .820 Density, lbs./cu.ft. 42.4 42.9 42.6 Water Absorption 12.6 l2.4 12.3 Internal bond, psi. 93 I58 I EXAMPLE 9 procedure of Example 1, aliquots of the pulerized furnish were treated with the respective compositions given in Table II in amounts corresponding to 6% total solids based on the weight of oven-dried wood, Casco WS-l 38 13 being a non-catalyzed urea-formaldehyde resin of commerce and containing 68% solids. Boards having the stated thickness and density were prepared by pressing at 330F. for 5 minutes at 5065() psi. The test results of the table show that the use of the method of this invention as exemplified in Experiment C in which 8. l% of the resin solids were replaced by sodium chloride resulted in superior modulus of rupture. Furthermore, although the treatmentbf Experiment C did not include addition of conventional ammonium sulfate catalyst, the products were comp'arable in regard to both internal strength and water absorption.

Mixtures were prepared of I00 grams of Casco Resin WS-l 3844 with 0.10 moles respectively of sodium chloride (NaCl), sodium bromide (NaBr), potassium chloride (KCI), potassium iodide (KI) and lithium chloride (LiCl). The mixture with sodium chloride was in the same proportions by weight as in Example 7. Treatments of pine chips were made according to the procedure of Example 7., the combined resin and halide solids amounting to 5.5% on dry-wood basis, and the paraffin wax solids amounting to 0.5% on the same basis. Boards were pressed for 4.5 minutes at 325F. and 50-650 psi. The test results summarized in Table IV further illustrate the advantages of the instant invention. In all cases substantial increases were achieved in internal bond strength and rupture modulus.

Table IV Comparison of Various Alkali Halides at Level 0.10 Moles per 100 grams UF Resin Alkali Halide None NaCl NaBr KC] Kl LiCl Board thickness, inches .814 .802 .810 .804 .805 .832 Density lhs./cu.ft. 42.2 42.6 42.0 42.7 42.2 40.9 Internal bond, psi. 55 124 137 138 142 138 Modulus of rupture, psi. 171 l 1877 1850 1963 1888 1744 Water ahsorption.'7( 16.6 16.9 26.2 15.5 21.2 9.1

EXAMPLE 10 furnish was treated with Casco Resin WS- 1- 14-79 and The effect of several levels of sodium chloride in the use of the instant invention is illustrated in Table V. The furnish was 100% pine, the sodium chloride was applied as a separate water solution to the chips which were then redried to the same moisture content as the control furnish before resin application. The procedure of Example 8 was followed, pressing at 325F. for 4.5 minutes under 50-650 psi.

a modification as summarized in the table below. Application was as described in Example 1. Amounts applied, based on oven-dry wood, were 6% of combined resin and halide solids and 0.5% of paraffin wax solids. Pressing was for 4 minutes at 320F.

The tests reported in Table Vll demonstrate substantial improvement in bond strength and waterabsorption properties.

Table VII A furnish was prepared from 80 parts planer shavings, containing Douglas Fir and Hemlock in the proportion of about 73/27, and parts of trim from 100% Douglas Fir protein-bonded plywood. Treatments of this furnish were made with UF Resin, Casco Resin WS13844 and modifications as summarized in Table VI. Application was carried out as described in Example 1. Amounts applied, based on oven-dried wood, were 6% of combined resin and halide solids, and 0.5% of paraffin wax solids. Pressing was for 4 minutes at 320F.

The tests reported in Table VI demonstrate substan tial improvement in internal bond strength and modu lus of rupture without seriously impairing water absorption.

Table VI Effect of Alkali Halide Replacement on Adhesive Efficiency of UP Resin Applied to Furnish Containing 20% Plywood Trim A furnish was prepared from 70 parts of Bauer Re-; fine Ponderosa Pine Douglas Fir (75/25) planer shavings and parts hammermilled plywood trim. The trim was from pine faced-white fir core production plywood bondcd with an exterior phenolic adhesive. This Effect of MgCl: addition on adhesive efl'icicncy 01' resin applied to furnish containing 30'/( plywood trim A urea aldehyde resin is prepared in the following steps:

a. A reactor vessel is charged with 25 parts of 50% aqueous formaldehyde, 20.5 parts acetaldehyde and 23 parts urea.

b. The pH is adjusted to 7.08.0 and the mixture is heated to reflux for one hour.

c. The pH is adjusted to 6.0 and condensation is continued until Gardner Bubble Tube reading is B.

d. After adjustment of pH to 7.0, there is added 12 parts of urea and the mixture is cooled to 30C.

e. One-half of the product of step (d) is mixed with 6 parts of a 66.7% slurry of sodium chloride in water.

EXAMPLE 14 In a series of corresponding preparations, the proce dure of Example 13 is followed excepting that the acetaldehyde is replaced by cquimolar amounts of respec-' tively propionaldehyde, butyraldehyde and furfural.

EXAMPLE. 15

The procedure of Example'13 is followed excepting that 50% of each addition of urea is replaced by melamine.

EXAMPLE 16 The various urea aldehyde resins corresponding to the products of steps (d) and (e) respectively of Examples 13, 14 and are used to treat pine chips according to the procedure of Example 1. The solids add-on in all cases is 6% on basis of oven-dry wood, and the curing conditions are identical throughout. The internal bond strength of each particle board is measured and it is found that each sample prepared with a product of step (e) has a significantly higher strength than the corresponding sample prepared with the control (d).

EXAMPLE 1 7 A plywood adhesive is prepared by mixing with 225 lbs. water at 55F., 165 lbs. of urea formaldehyde resin Casco Resin SH, 188 lbs. of wheat flour, 9 lbs. soluble blood and 2 lbs. of an anti-foaming agent, Defoamer AF-3 l. A modification of this adhesive also is prepared wherein 5% of the urea-formaldehyde resin solids are replaced by sodium chloride.

These adhesives are used respectively to construct plywood panels on a laboratory scale, assembling five inner plies of 1/7 inch white fir veneers dried to 3% moisture content and two-face plies of H24 inch birch veneers dried to 8% moisture content. In each case both sides of three of the inner plies are treated with 34.5 lbs. per l000 sq. ft. of the same adhesive. The assembled panel is prepressed at 175 psi. and then hotpressed at 175 psi. for 5.5 minutes at 260F. Total assembly time is 45 minutes.

Both adhesives are equally effective in producing suitable panels with the adhesive of the instant invention having the commercial advantage of being much less costly.

It will be understood that it is intended to cover all changes and modifications of the examples of the invention herein chosen for the purpose of illustration which do not constitute departures from the spirit and scope of the invention.

What is claimed is:

l. The process of making particle board which comprises a. treating wood flakes with an aqueous adhesive solution so as to deposit approximately 3-15 parts of solids per parts by weight of wood, said solids consisting essentially of a urea-formaldehyde resin and a material selected from the group consisting of sodium chloride and a mixture of sodium and magnesium chlorides, the material being present in an amount from about 1 to about 35% by weight of the total urea-formaldehyde and material solids.

b. consolidating the resulting mass under pressure to desired shape, and

c. exposing the mass to a temperature of from about 280 to 425F. for about 2-20 minutes to cure the resin.

2. The process of claim 1 wherein the step of consolidating is carried out at a pressure of 50 to 800 psi.

3. The process of claim 1 Wlherein from 5 to 50% of urea is replaced by melamine.

4. The process of claim 1 wherein the wood flakes contain up to 50% weight of waste material selected from peeler cores, veneer residues, plywood trim, slats, edgings and mixtures thereof.

5. Process of claim 1 wherein the lower limit on amount of said material is about 3% by weight of the total urea-formaldehyde and material solids.

6. The process of claim 1 wherein said material is so dium chloride. 

1. THE PROCESS OF MAKING PARTICLE BOARD WHICH COMPRISES A. TREATING WOOD FLAKES WITH AN AQUEOUS ADHESIVE SOLUTON SO AS TO DEPOSIT APPROXIMATELY 3-15 PARTS OF SOLIDS PER 100 PARTS BY WEGHT OF WOOD, SAID SOLIDS CONSISTING ESSENTIALLY OF A UREA-FORMALDEHYDE RESIN AND A MATERIAL SELECTED FROM THE GROUP CONSISTING OF SODIUM CHLORIDE AD A MIXTURE OF SODIUM AND MAGNESIUM CHLORIDES, THE MATERIAL BEING PRESENT IN AN AMOUNT FROM ABOUT 1 TO ABOUT 35% BY WEIGHT OF THE TOTAL UREA-FORMALDEHYDE AND MATERIAL SOLIDS. B. CONSOLIDATING THE RESULTING MASS UNDER PRESSURE TO DESIRED SHAPE, AND C. EXPOSING THE MASS TO A TEMPERATURE OF FROM ABOUT 280* TO 425*F FOR ABOUT 2-20 MINUTES TO CURE THE RESIN.
 2. The process of claim 1 wherein the step of consolidating is carried out at a pressure of 50 to 800 psi.
 3. The process of claim 1 wherein from 5 to 50% of urea is replaced by melamine.
 4. The process of claim 1 wherein the wood flakes contain up to 50% weight of waste material selected from peeler cores, veneer residues, plywood trim, slats, edgings and mixtures thereof.
 5. Process of claim 1 wherein the lower limit on amount of said material is about 3% by weight of the total urea-formaldehyde and material solids.
 6. The process of claim 1 wherein said material is sodium chloride. 